High permeability composite films to reduce noise in high speed interconnects

ABSTRACT

This invention provides a structure and method for improved transmission line operation on integrated circuits. One method of the invention includes forming transmission lines in an integrated circuit. The method includes forming a first layer of electrically conductive material on a substrate. A first layer of insulating material is formed on the first layer of the electrically conductive material. A pair of high permeability metal lines are formed on the first layer of insulating material. The pair of high permeability metal lines include composite hexaferrite films. A transmission line is formed on the first layer of insulating material and between and parallel with the pair of high permeability metal lines. A second layer of insulating material is formed on the transmission line and the pair of high permeability metal lines. And, the method includes forming a second layer of electrically conductive material on the second layer of insulating material.

RELATED APPLICATION(S)

This application is a Divisional of U.S. application Ser. No. 10/099,020filed on Mar. 13, 2002 which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to integrated circuits. Moreparticularly, it pertains to structure and methods for improvedtransmission line interconnections.

BACKGROUND OF THE INVENTION

The metal lines over insulators and ground planes, or metal lines buriedin close proximity to dielectric insulators and used for integratedcircuit interconnects are in reality transmission lines or strip lines.The use of coaxial interconnection lines for interconnections throughthe substrate in CMOS integrated circuits can also be termedtransmission lines or strip lines. Interconnection lines on interposersor printed circuit boards can also be described as transmission lines.

The low characteristic impedance of any of these lines, transmission,strip lines or coaxial lines results in part from the low characteristicimpedance of free space, Zo=(μ_(o)/ε_(o))^(1/2)=377 ohms, and in partfrom the dielectric material used for electrical insulation in the lineswhich has a higher dielectric permittivity than free space. Mostcommonly used coaxial lines have an impedance of 50 ohms or 75 ohms, itis difficult to achieve larger values. In the past these effects havenot received much consideration on the integrated circuits themselvessince the propagation speed with oxide insulators is 15 cm/ns andswitching speeds on integrated circuits of the size of a centimeter havebeen slower than {fraction (1/15)} ns or 70 picoseconds. Transmissionline effects only become important if the switching time is of the sameorder as the signal propagation time. Switching times in CMOS circuitshave been limited by the ability to switch the capacitive loads of longlines and buffers, and charge these capacitances over large voltageswings to yield a voltage step signal.

Most current CMOS integrated circuit interconnections rely on thetransmission of a voltage step or signal from one location to another.FIG. 1 illustrates R-C limited, short high impedance interconnectionswith capacitive loads. The driver may simply be a CMOS inverter as shownin FIG. 1 and the receiver a simple CMOS amplifier, differentialamplifier, or comparator.

As shown in FIG. 1, the CMOS receiver presents a high impedancetermination or load to the interconnection line. This is problematic inthat:

(i) the switching time response or signal delay is determined mainly bythe ability of the driver to charge up the capacitance of the line andthe load capacitance,

(ii) the line is not terminated by its characteristic impedanceresulting in reflections and ringing,

(iii) large noise voltages may be induced on the signal transmissionline due to capacitive coupling and large voltage swing switching onadjacent lines, the noise voltage can be a large fraction of the signalvoltage.

The transmission of voltage step signals only works well if theinterconnection line is short so that the stray capacitance of the lineis small. Long lines result is slow switching speeds and excessive noisedue to capacitive coupling between lines.

FIG. 1 shows the commonly used signal interconnection in CMOS integratedcircuits, where voltage signals are transmitted from one location toanother. This is problematic in that the interconnection lines arenormally loaded with the capacitive input of the next CMOS stage and thelarge stray capacitance of the line itself. The response time isnormally slow due to the limited ability of the line drivers to supplythe large currents needed to charge these capacitances over largevoltage swings. These times are usually much larger than the signaltransmission time down the line so a lumped circuit model can be used tofind the signal delay, as shown in FIG. 1.

In the example here the output impedance of the source follower is1/gm=1000 ohms, and a line 0.1 cm long will have a capacitance of about0.2 pF if the dimensions of the line are about 1 micron by 1 micron andthe insulator or oxide thickness under the line is 1 micron. Thisresults in a time constant of 200 pS and it takes about 400 pS to chargethe line from 10% to 90% of the final voltage value. This is arelatively slow response.

Furthermore, if two interconnection wires are in close proximity thenthe voltage swing on one line can induce a large voltage swing or noisevoltage on the adjacent line as shown in FIG. 1. The noise voltage isjust determined by the capacitance ratios, or ratio of interwirecapacitance, Cint, to the capacitance of the interconnection wire, C.

In prior art these can be comparable, as shown, and depend on theinsulator thickness under the wires and the spacing between the wires.Therefore, the noise voltage can be a large fraction of the signalvoltage if the wires are in close proximity and far removed from thesubstrate by being over thick insulators. The emphasis in prior art hasalways been in trying to minimize the capacitance of the interconnectionline, C, by using thick insulators and low dielectric constantmaterials.

Thus, there is a need to provide a solution for these types of problemsfor CMOS-scaled integrated circuits. Due to the continued reduction inscaling and increases in frequency for transmission lines in integratedcircuits such solutions remain a difficult hurdle. For these and otherreasons there is a need to reduce noise in high speed interconnections.

SUMMARY OF THE INVENTION

The above mentioned problems with CMOS line interconnections as well asother problems are addressed by the present invention and will beunderstood by reading and studying the following specification. Highspeed interconnections are provided which accord exemplary performance.That is, the invention described here provides an improved andefficiently fabricated technique for high speed transmission lines onCMOS integrated circuits. In addition, the novel low input impedanceCMOS circuit offers the following advantages: (1) the signal delaydepends only on the velocity of light on the line and is easilypredictable and reproducible, eliminating or allowing for compensationfor signal and/or clock skew, (2) there are no reflections at thereceiving end of the line and this minimizes ringing, and (3) noisesignals will be smaller due to weaker coupling between lines resultingin better signal to noise ratios, the noise current will only be a smallfraction of the signal current.

One embodiment of the invention includes a method for formingtransmission lines in an integrated circuit. The method includes forminga first layer of electrically conductive material on a substrate. Afirst layer of insulating material is formed on the first layer of theelectrically conductive material. A pair of high permeability metallines are formed on the first layer of insulating material. The pair ofhigh permeability metal lines include composite hexaferrite films. Atransmission line is formed on the first layer of insulating materialand between and parallel with the pair of high permeability metal lines.A second layer of insulating material is formed on the transmission lineand the pair of high permeability metal lines. And, the method includesforming a second layer of electrically conductive material on the secondlayer of insulating material.

These and other embodiments, aspects, advantages, and features of thepresent invention will be set forth in part in the description whichfollows, and in part will become apparent to those skilled in the art byreference to the following description of the invention and referenceddrawings or by practice of the invention. The aspects, advantages, andfeatures of the invention are realized and attained by means of theinstrumentalities, procedures, and combinations particularly pointed outin the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the commonly used signal interconnection in CMOS integratedcircuits, where voltage signals are transmitted from one location toanother.

FIG. 2 illustrates one technique to minimize the interwire capacitance,Cint, by using an intermediate line at ground for shielding.

FIG. 3A illustrates signal transmission using correctly terminatedtransmission lines and current sense amplifiers, according to theteachings of the present invention.

FIG. 3B illustrates two interconnection lines in close proximity and theinterwire capacitance between these lines and the mutual inductancecoupling between the lines.

FIG. 4 is a perspective view illustrating a pair of neighboringtransmission lines above a conductive substrate, according to theteachings of the present invention.

FIG. 5 is a schematic diagram for an interconnection on an integratedcircuit according to the teachings of the present invention.

FIG. 6 illustrates one embodiment for a pair of neighboring transmissionlines, according to the teachings of the present invention.

FIG. 7 illustrates another embodiment for a pair of neighboringtransmission lines, according to the teachings of the present invention.

FIG. 8 illustrates another embodiment for a pair of neighboringtransmission lines, according to the teachings of the present invention.

FIG. 9 illustrates another embodiment for a pair of neighboringtransmission lines, according to the teachings of the present invention.

FIG. 10 illustrates another embodiment for a pair of neighboringtransmission lines, according to the teachings of the present invention.

FIG. 11 illustrates another embodiment for a pair of neighboringtransmission lines, according to the teachings of the present invention.

FIG. 12 illustrates another embodiment for a pair of neighboringtransmission lines, according to the teachings of the present invention.

FIG. 13 is a block diagram which illustrates an embodiment of a systemusing line signaling according to teachings of the present invention.

FIG. 14 is a block diagram which illustrates another embodiment of asystem according to teaching of the present invention.

DETAILED DESCRIPTION

In the following detailed description of the invention, reference ismade to the accompanying drawings which form a part hereof, and in whichis shown, by way of illustration, specific embodiments in which theinvention may be practiced. In the drawings, like numerals describesubstantially similar components throughout the several views. Theseembodiments are described in sufficient detail to enable those skilledin the art to practice the invention. Other embodiments may be utilizedand structural, logical, and electrical changes may be made withoutdeparting from the scope of the present invention.

The terms wafer and substrate used in the following description includeany structure having an exposed surface with which to form theintegrated circuit (IC) structure of the invention. The term substrateis understood to include semiconductor wafers. The term substrate isalso used to refer to semiconductor structures during processing, andmay include other layers that have been fabricated thereupon. Both waferand substrate include doped and undoped semiconductors, epitaxialsemiconductor layers supported by a base semiconductor or insulator, aswell as other semiconductor structures well known to one skilled in theart. The term conductor is understood to include semiconductors, and theterm insulator is defined to include any material that is lesselectrically conductive than the materials referred to as conductors.The following detailed description is, therefore, not to be taken in alimiting sense, and the scope of the present invention is defined onlyby the appended claims, along with the full scope of equivalents towhich such claims are entitled.

FIG. 2 illustrates one technique to minimize the interwire capacitance,Cint, by using an intermediate line at ground for shielding. Thistechnique is disclosed in a co-pending application by a common inventor,Dr. Leonard Forbes, entitled “Novel Transmission Lines for CMOSIntegrated Circuits,” Ser. No. 09/364,199. The same is incorporatedherein by reference.

Also, as disclosed in issued U.S. Pat. No. 6,255,852 by Dr. LeonardForbes, entitled “Current Mode Interconnects on CMOS IntegratedCircuits,” low impedance transmission lines such as those which exist onCMOS integrated circuits are more amenable to signal currentinterconnections over longer interconnection lines. U.S. Pat. No.6,255,852 is incorporated herein by reference. These longerinterconnection lines may be on the CMOS integrated circuit itself, aninterconnection line between integrated circuits mounted in a module asfor instance a memory module, an interposer upon which these integratedcircuits are mounted, or on a printed circuit board upon which theintegrated circuits are mounted. If the line is terminated with a lowinput impedance current sense amplifier then the line can be regarded asa transmission line terminated with the characteristic impedance of theinterconnection line. This is advantageous in that:

(i) the signal delay depends only on the velocity of light on the lineand is easily predictable and reproducible, eliminating or allowing forcompensation for signal and/or clock skew,

(ii) there are no reflections at the receiving end of the line and thisminimizes ringing,

(iii) noise signals will be smaller due to weaker coupling between linesresulting in better signal to noise ratios, the noise current will onlybe a small fraction of the signal current. The transmission of currentsignals rather than voltage signals is more desirable at high speeds,and in high speed or high clock rate circuits over longerinterconnection lines. A CMOS circuit might for instance use acombination of techniques, conventional voltage signals over shortinterconnections with little coupling between lines and current signalsover longer interconnections and where lines might be in closeproximity.

FIG. 3A illustrates capacitive coupling between low impedance terminatedinterconnection lines. FIG. 3A illustrates signal transmission usingcorrectly terminated transmission lines and current sense amplifiers,such as those disclosed in issued U.S. Pat. No. 6,255,852 by Dr. LeonardForbes, entitled “Current Mode Interconnects on CMOS IntegratedCircuits.” The signal interconnection or transmission line is terminatedby the matching impedance of the current sense amplifier. This means theimpedance looking into the sending end of the transmission line willjust be the characteristic impedance of the line and the signal delaydown the line will just be the small propagation delay down the line.The response time of the source follower being used as a line driverwill be determined primarily by the longer rise time of the inputvoltage. This driver will supply a signal current whose rise time isbasically just that of the input voltage signal.

FIG. 3A also illustrates the coupling to another signal line in closeproximity, in this case the coupling will be both magnetic through theinduced magnetic fields and mutual inductance and capacitive coupling.The noise current induced will be shown to be only a fraction of thesignal current or the signal to noise ratio is high. Once received thissignal current is converted back to a signal voltage by the currentsense amplifier at the receiving end of the line. Since the signalpropagation time is small, the signal delay time will in practice belimited by the rise time of the signal to the gate of the sourcefollower. Since the gate capacitance of the source follower is smallthis can be very fast.

Other methods to minimize capacitive coupling between lines use lowdielectric constant materials or insulators, or ground shields, such asshown in FIG. 2. In the present invention, it is desirable to use verylow impedance lines, it is also desirable to keep the capacitivecoupling between lines small and the magnitude of voltage steps on theinterconnection lines small. The current step will induce a voltage stepat the load which is the magnitude of the load impedance times thiscurrent step. This voltage step while small, 1 mA times Zin in thisexample, still can induce a capacitively coupled noise signal on anadjacent line.

FIG. 3A shows an integrated circuit 300 in which a first transmissionline, strip line, or coaxial line 301A interconnects circuit components,e.g. a driver 310 to a receiver 320. FIG. 3A illustrates a firsttransmission line 301A over a conductive substrate 305. Conventionally,a voltage signal (i.e. a 5 volt signal swing) is provided by the driver310 to the transmission line 301A. The schematic illustrations in FIG.3A demonstrate that the transmission line 301A includes a smallresistance, shown generally by resistor symbols 302A, 302B, . . . ,302N. Also, the transmission line 301A includes a distributed inductance(L) which is represented generally by inductor symbols 303A, 303B, . . ., 303N. In one embodiment, the driver 310 may be an inverter 310 and thereceiver 320 may be an amplifier 320. Capacitor plate symbols 304 (C)are used to schematically represent the capacitive coupling which occursbetween the transmission line 301A and the conducting substrate 305. InFIG. 3A, a second transmission line 301B is shown. Capacitor platesymbols 306 are used to schematically represent the capacitive coupling(Cint) which similarly occurs between the first transmission line 301Aand neighboring transmission lines, e.g. second transmission line 301B.

FIG. 3B illustrates two interconnection lines in close proximity and theinterwire capacitance between these lines and the mutual inductancecoupling between the lines. (See generally, H. Johnson, “High-SpeedDigital Circuits: A Handbook of Black Magic,” Prentice-Hall, 1993; andS. Ramo, J. R. Whinnery and T. Van Duzer, “Fields and Waves inCommunication Electronics, 3rd Ed.,” John Wiley, New York, 1994).Although the interconnection lines on integrated circuits might tend tobe more square than round, the concepts involved can be mostconveniently described and formulas approximated by assuming forsimplicity that the lines are round or circular. Approximate formulashave been developed describing round wires over conductive planes or twowires in close proximity, in this case they are interconnection wires ona CMOS integrated circuit, interposer, or printed circuit board.

In FIG. 3B the illustrated pair of interconnect, or transmission lines,301A and 301B, displayed in a perspective view, are separated from aconducting substrate 305. The transmission lines, 301A and 301B arespaced a distance (h) from the conducting substrate 305 and a distance(s) from one another. The transmission lines, 301A and 301B, are shownin a circular geometry, each with a diameter (a). Some generalcharacterizations can be made about the transmission lines, 301A and301B, in an environment floating or suspended in air. First, eachtransmission line, 301A and 301B, will have a characteristic impedancein air (Z₀) approximately or generally given by Z₀≅60 ln(4h/a). Second,each transmission line, 301A and 301B, has a inductance (L) which isL≅5.08×10⁻⁹×ln(4h/a) Henrys/inch (H/inch). Additionally, the twotransmission lines, 301A and 301B, will exhibit an interwire mutualinductance (M) which is given by M=L×{1/[1+(s/h)²]}. Third, an interwirecapacitive coupling (Cint) exists between the two transmission lines,301A and 301B, and is expressed as Cint=π∈/cosh⁻¹(s/a). Using thetrigonometric relationship of cosh⁻¹(y)≅ln(2y), the interwire capacitivecoupling can similarly be expressed as Cint≅π∈/ln(2s/a). Thus, in thisenvironment, the two transmission lines, 301A and 301B, exhibit aninterline capacitance (Cint) given by Cint={0.7/[ln(2 s/a)]}picoFarads/inch (pF/inch). Lastly, each transmission line, 301A and 301B,will further exhibit capacitive coupling C with the conducting substrate305.

Again, in FIG. 3B the transmission lines, 301A and 301B, are spaced adistance (h) from the conducting substrate 305. Using the method ofimages and the interwire capacitive relationship, Cint≅π∈/ln(2 s/a), asingle transmission line, 301A, over a conducting substrate is given byC≅2π∈/ln(4h/a)pF/inch where h≅s/2. Thus, in this environment, the twotransmission lines, 301A and 301B, exhibit a capacitance, or capacitivecoupling C with the conductive substrate 305 which isC≅{1.41/[ln(4h/a)]}pF/inch. The above equations have been presented byassuming that the transmission lines have round or circular geometries.Actual transmission lines on integrated circuits might tend to be moresquare or rectangular than round due to present lithography techniques.Nevertheless, due to the actual physical size of transmission lines,determined according to minimum lithographic feature techniques, theformulas scale well to square, rectangular or other physical crosssectional geometries for the transmission lines.

The signal rise time (trise) in conventional voltage signaling isnormally slow due to the limited ability of the transmission linedrivers to supply the large currents needed to charge these capacitancesover large voltage swings. The signal rise times are usually much largerthan the signal transmission time down the line (tprop). Additionally,if two transmission lines are in close proximity then the voltage swingon one transmission line can induce a large voltage swing or noisevoltage on the adjacent transmission line. The noise voltage isdetermined by the capacitance ratios of interwire capacitance, Cint, tothe capacitance of the transmission line with the substrate, C. In otherwords, the noise voltage is determined according to the ratio Cint/C.

The values of Cint and C can be comparable, dependant upon the insulatorthickness (h) under the transmission lines and the spacing between thetransmission lines. Emphasis in prior art is placed upon minimizing thecapacitance of the transmission line, C, by using thick insulators andlow dielectric constant materials. Emphasis is also to some extentplaced upon minimizing the interwire capacitance, Cint. Thus, theapproach in the prior art results in a noise voltage which can be alarge fraction of the signal voltage if the transmission lines are inclose proximity and far removed from the substrate by being over thickinsulators.

FIG. 4 is a perspective view illustrating a pair of neighboringtransmission lines, 401A and 401B, above a conductive substrate 405according to the teachings of the present invention. The presentinvention is designed to use current signaling across low impedancetransmission lines, 401A and 401B, to reduce signal transmission delayand to improve signaling performance over longer transmission lines.Under conventional voltage signaling the current provided in thetransmission lines is too weak to provide clean, accurately detectablecurrent signal. In order to obtain better current signals in thetransmission lines the signal to noise ratio of the transmission linesmust be improved.

To improve the signal to noise ratio of the transmission lines, 401A and401B, the capacitance coupling between the transmission lines, 401A and401B, and the conductive substrate 405, is made large. Thecharacteristic impedance (Zo) of the transmission lines, 401A and 401B,can be expressed as Z₀=√{square root over (L/C)}. Thus, making C largemakes the characteristic impedance Zo=Zin, small and similarly makes thevoltage division ratio for capacitive coupling small. In the presentinvention, C increases as the insulator 407 thickness (h) separating thetransmission lines, 401A and 401B, from the ground plane, or substrate405 is decreased. In FIG. 4, the transmission lines, 401A and 401B, areseparated a distance (h) from the conducting substrate 405 by aninsulating layer 407. In one embodiment, the insulating layer 407 is anoxide layer 407. The capacitive coupling C between the transmissionlines, 401A and 401B, and the conducting substrate 405 separated by anoxide layer 407 is given as C≅1.66/[ln(4h/a)]pF/cm. Additionally, theinductance (L) for the transmission lines, 401A and 401B, over the oxidelayer 407 is L≅2×ln(4h/a)nanoHenrys/centimeter (nH/cm). The transmissionlines, 401A and 401B, are shown in a square geometry having a width (a).The insulator 407 has a thickness (b) separating the transmission lines,401A and 401B from the substrate. 405. According to one embodiment ofthe present invention, the insulator thickness (b) is made thinner thanthe thickness (t) of the transmission lines, 401A and 401B. The centerof the transmission lines, 401A and 401B, are a distance (h) above theconducting substrate 405.

According to the teachings of the present invention, in one embodimentthe thickness (b) of the insulator is equal to or less than 1.0micrometers (μm). In one embodiment, the thickness (t) of the of thetransmission lines, 401A and 401B is approximately equal to 1.0micrometers (μm). In one embodiment, the thickness (t) of thetransmission lines, 401A and 401B is less than 1.0 (μm). In oneembodiment, the width (a) of the transmission lines, 401A and 401B isapproximately 1.0 micrometers (μm). As one of ordinary skill in the artwill appreciate upon reading the present disclosure, one embodiment ofthe present invention includes transmission lines 401A and 401B formedaccording to the above described dimensions and separated from thesubstrate 405 by an insulator having a thickness (b) of less than 1.0micrometers (μm). In one exemplary embodiment, the transmission lines401A and 401B have an input impedance (Z₀) approximately equal to 50ohms.

A co-pending application, by the same inventors, entitled “CapacitiveTechniques to Reduce Noise in High Speed Interconnections,” applicationSer. No. ______, describes minimizing interwire coupling capacitance,and making the insulator thickness over the group plane small,minimizing Zo. The same is incorporated herein by reference. Accordingto the teachings described therein, a characteristic impedance of 50ohms is easily realizable.

FIG. 5 is a schematic diagram for an interconnection on an integratedcircuit 500 according to the teachings of the present invention. Theinterconnection on the integrated circuit 500 includes a pair oftransmission lines, 501A and 501B, in close proximity. The firsttransmission line 501A is separated by a distance (s) from the secondtransmission line 501B. The first transmission line 501A and the secondtransmission line 501B each have a first end, 505A and 505Brespectively. In one embodiment, the first end 505A for the firsttransmission line 501A is coupled to a driver 503. The firsttransmission line 501A and the second transmission line 501B each have asecond end, 506A and 506B respectively. In one embodiment, the secondend 506A is coupled to a termination 504 formed using a complementarymetal oxide semiconductor (CMOS) process.

Reference to FIG. 5 is useful in explaining the reduced amount of noisecurrent between two transmission lines, 501A and 501B, using the currentsignaling technique of the present invention. In one embodiment of thepresent invention, transmission lines, 501A and 501B, have a lowcharacteristic impedances Zo. In one embodiment, the input impedance(Zin) seen by the driver 503 coupling to the first transmission line501A (in this example the “driven line”) is just the characteristicimpedance Zo for the first transmission line 501A. In other words, theCMOS termination 504 is impedance matched to the characteristicimpedance Zo of the transmission line 501A.

In one embodiment, the first transmission line 501A is separated byapproximately 3 μm from the second transmission line 501B and thetransmission lines have a length (l) of at least 500 μm. In anotherembodiment the transmission lines, 501A and 501B, have a length (l) ofat least 0.1 cm, or 1000 μm. As in FIG. 4, the transmission lines, 501Aand 501B, are separated from a conducting substrate by an insulatinglayer. In one embodiment, the insulating layer is an oxide layer. Inthis embodiment, the capacitive coupling C between the transmissionlines, 501A and 501B, and the conducting substrate is given asC≅1.66/[ln(4h/a)]pF/cm. In one exemplary embodiment, each transmissionline, 501A and 501B, has a length (l) of 0.1 cm or 1000 μm, each has awidth (a) of approximately 1.0 μm, and the insulator layer thickness (b)is approximately 0.2 μm. In this embodiment, the ln(4h/a) will beapproximately 1. Thus, C≅1.66/[ln(4h/a)]pF/cm and for a line 0.1 cm longwill produce a C≅0.2 pF. In the same embodiment, the inductance (L) forthe transmission lines, 501A and 501B, over the oxide layer isL≅2×ln(4h/a) nH/cm, or L=0.2 nH for a line 0.1 cm long. In thisembodiment, a 1 milli Ampere (mA) current step, i₁(t), is applied to thegate 502 of a transistor driver 503. In one embodiment, the driver is ann-channel source follower driver 503. In this embodiment, the rise time(trise) on the gate 502 of the driver 503 is approximately 100 ps. Thisis the limiting time on the system response since the signal delay(tprop) down a the transmission line is proportional to √{square rootover (LC)}. For a 0.1 cm transmission line, 501A or 501B, tprop is only7 ps. A current, di₁(t)/dt, of approximately 1×10⁷ A/sec is thenproduced on the first transmission line 501A.

The noise current i₂(t) induced on the second transmission line 501B byinterwire capacitive coupling (Cint) is calculated as approximatelyi₂(t)=(Cint)×(V₁step/trise). The interwire capacitive coupling (Cint)between the transmission lines, 501A and 501B, separated by an oxidedielectric can be expressed as Cint=0.46 pF/cm. Again, for a 0.1 cmtransmission line, 501A or 501B, Cint≅0.05 pF. As described inconnection with FIG. 5, a 1 mA current provided to the firsttransmission line 501A having a low characteristic impedance Zo ofapproximately 30 Ohms will result in a corresponding 30 mV Voltage step(V₁step) on the first transmission line 501A. Therefore, if trise is 100ps a noise current, i₂(t), of approximately 0.015 mA is produced on thesecond, neighboring, transmission line 501B. This noise current, i₂(t),induced in the second transmission line 501B is a very small percentage,or about 1%, of the signal current i₁(t) provided to the firsttransmission line 501A. Hence, the signal to noise ratio (SNR) will belarge. It can be shown, in general, that a signal to noise ratio (SNR)for the present invention, due to capacitive coupling is of the order(C/Cint) (trise/tprop); where, trise, is the rise time for the currentsignal and, tprop, the signal propagation time down the firsttransmission line 501A. The rise time on the signal current, i₁(t), inthe first transmission line 501A is fast and just follows the rise time(trise) on the input signal, or 100 ps. The response time of this systemutilizing current signals is thus much faster than those using voltagesignals.

Reference to FIG. 5 is similarly useful to illustrate the noise voltagesignal from magnetic coupling induced in the second transmission line501B by the signal current in the first transmission line 501A. As shownin FIG. 5, a voltage will be induced in the second transmission line501B which has a magnitude that depends on the trise, di₁(t)/dt, of thecurrent i₁(t) in the driven transmission line 501A, and the mutualinductance coupling (M) between neighboring transmission lines, e.g.501A and 501B. Each transmission line, 501A and 501B, has an inductance(L). As stated above, L≅0.2 nH for a 0.1 cm transmission line, 501A and501B. In one exemplary embodiment, the current i₁(t) in the firsttransmission line, 501A (in this example the “driven line”) rises to 1mA in 100 ps. A current, di₁(t)/dt, of approximately 1×10⁷ A/sec is thenproduced on the first transmission line 501A. As presented above inconnection with FIG. 3A and 3B, the mutual inductance coupling (M) canbe expressed as M=L×{1/[1+(s/h)²]}. In one exemplary embodiment, s isapproximately equal to 3 μm, and h is approximately equal to 0.7 μm. Inthis embodiment, M will equate to approximately M=0.02 nano Henrys (nH).

Using the relationship that the induced voltage (Vind)=M×di₁(t)/dt, Vindis approximately equal to 0.2 mV. During this 100 ps time period theinduced voltage traveling down the second transmission line 501B justsees the characteristic impedance Zo of the second transmission line501B. In one embodiment Zo is approximately 30 Ohms, so here, thecurrent induced i₂(t) in the second transmission line is i₂(t)=Vind/Zoor 0.007 mA. This low value current is only approximately one percent(1%) of the signal current i₁(t) on the first transmission line, 501A.Hence, a large signal to noise ratio (SNR) results. In contrast, underthe prior technology, if high impedance capacitive loads had been usedon high characteristic impedance lines and conventional voltagesignaling employed there is typically a large noise voltage between theneighboring transmission lines, 501A and 501B. In the prior technology,the large noise voltage can be about one half as big as signal voltages.

The second transmission line 501B has an equivalently rapid timeconstant, (L/R) to that of the first transmission line 501A. In theembodiment presented above, the time constant is approximately 7 picoseconds (ps). The noise current i₂(t) in the second transmission line501B will reach a steady state in that time constant. The noise currentstays at this steady state value until the end of trise, in thisembodiment 100 ps, at which point i₁(t) stops changing. After this, thenoise current in the second line decays away very quickly. Again, whenthe input impedance seen by the driver 503 is matched to thecharacteristic impedance Zo of the first transmission line 501A, thesignal to noise ratio (SNR) due to inductive coupling between the firsttransmission line 501A and the second, or neighboring, transmission line501B is of the order, (L/M) (trise/tprop). In other embodiments, theactual mutual inductance and self inductances may vary from these givenvalues without departing from the scope of the invention.

Inductive effects which become important at high speeds include not onlythe self inductance of the interconnection lines, L, but also the mutualinductance between lines, M. As shown with respect to FIG. 5, previouslythe signal-to-noise ratio due to inductive coupling between lines is ofthe order, (L/M)(trise/tprop). Any technique which will minimize themutual inductance between lines will improve the signal-to-noise ratioon long interconnection lines in integrated circuits with high switchingspeeds.

The present invention, as described further below, provides structuresand methods through which inductive coupling on high speed interconnectscan be further reduced thus increasing the signal to noise ratio acrossthe same.

According to the teachings of the present invention, inductive couplingcan be minimized by:

(i) magnetic shields above and below the lines

(ii) magnetic shields between lines;

These magnetic shields may be:

(i) good conductors with a thickness greater than the skin depth, theconventional approach, but one which may not be possible or practicalwith interconnection lines of sub-micron dimensions

(ii) shields with high permeability metals to minimize the mutualcoupling or inductance between lines.

One embodiment of the invention, as discussed further below inconnection with FIG. 6, is a structure where an interconnection line islocated between a ground buss and a power supply buss (which for the ACsignal is AC ground) and as such constitutes a low impedancetransmission line interconnection. If the ground and power supply bussesare thicker than the skin depth at the frequency of interest, theelectric and magnetic fields will be shielded and confined to the areabetween these plates. As shown in the embodiment of FIG. 6, a layeredhigh permeability shielding line is placed between interconnection linesto distort the magnetic fields and shield the lines.

Other possible configurations are shown in FIGS. 7-12. Theseconfigurations highlight the fact that a single metal might not have allthe suitable properties for a given or desired implementation by systemsdesigned for low noise operation. For example, two materials might benecessary, one which has the desired magnetic properties to confinemagnetic fields and one to confine the electric fields. Accordingly,FIGS. 7-12 illustrate various alternative embodiments of the presentinvention as can be best suited to a particular system designed for lownoise operation. These embodiments make use of a sandwich layer of botha high permeability material, well suited for magnetic shielding, aswell as a low resistive conductive material that is well suited forelectrical shielding. By placing even a thin layer of the highpermeability material, a considerable amount of the magnetic field canbe contained.

FIG. 6 illustrates one embodiment for a pair of neighboring transmissionlines, 601A and 601B, according to the teachings of the presentinvention. FIG. 6 illustrates one or more transmission lines, shown as601A and 601B. The one or more transmission lines, 601A and 601B, arespaced between a pair of electrically conductive planes 604 and 605. Asone of ordinary skill in the art will understand upon reading thisdisclosure, in one embodiment at least one of the electricallyconductive planes is formed on a substrate. As one of ordinary skill inthe art will understand upon reading this disclosure, the substrate caninclude an insulator, a semiconductor material, silicon on insulatormaterial, or other materials. The invention is not so limited.

As shown in FIG. 6, the invention includes a number of high permeabilitymetal lines, shown in this embodiment as 602A and 602B. According to theteachings of the present invention, the number of high permeabilitymetal lines, 602A and 602B, are formed of composite hexaferrite films.As shown in FIG. 6, the number of high permeability metal lines, 602Aand 602B are interspaced between the one or more transmission lines,601A and 601B. In one embodiment of the present invention, the one ormore transmission lines, 601A and 601B, and the number or highpermeability metal lines, 602A and 602B, are spaced parallel to oneanother and are oriented lengthwise perpendicular to the plane of thepage illustrated in FIG. 6. In the invention, the one or moretransmission lines, 601A and 601B, and the number or high permeabilitymetal lines, 602A and 602B, are separated from one another and from thepair of electrically conductive planes 604 and 605 by an insulatormaterial 606. In one embodiment of the present invention, the insulatormaterial 606 includes an oxide.

In one embodiment as shown in FIG. 6, the pair of electricallyconductive planes 604 and 605 include metal ground planes 604 and 605.In the invention, the electrically conductive planes, 604 and 605, canbe independently coupled to a ground source and/or a power supply bus asthe same will be known and understood by one of ordinary skill in theart. In the embodiment shown in FIG. 6, at least one of the pair ofelectrically conductive planes, 604 and 605, is formed to a thickness(t) which is greater than a skin depth (sd) penetrable by electricallyinduced magnetic field lines.

As one of ordinary skill in the art will understand upon reading thisdisclosure, an electrical signal transmitted across the one or moretransmission lines, 601A and 601B will induce a magnetic fieldsurrounding the one or more transmission lines, 601A and 601B. In theembodiment of FIG. 6 such a magnetic field is illustrated by magneticfield lines 611. According to the teachings of the present invention,the number of high permeability metal lines, 602A and 602B, and theelectrically conductive planes, 604 and 605, provide magnetic shieldingto reduce the amount of magnetically induced noise on neighboringtransmission lines, e.g. 601A and 601B.

FIG. 7 illustrates another embodiment for a pair of neighboringtransmission lines, 701-1 and 701-2, according to the teachings of thepresent invention. FIG. 7 illustrates one or more transmission lines,shown as 701-1 and 701-2. The one or more transmission lines, 701-1 and701-2, are spaced between a pair of electrically conductive planes 704and 705. As one of ordinary skill in the art will understand uponreading this disclosure, any number of transmission lines, 701-1, . . ., 701-N, can be spaced between the conductive planes 704 and 705. As oneof ordinary skill in the art will understand upon reading thisdisclosure, in one embodiment at least one of the electricallyconductive planes is formed on a substrate. As one of ordinary skill inthe art will understand upon reading this disclosure, the substrate caninclude an insulator, a semiconductor material, silicon on insulatormaterial, or other materials. The invention is not so limited.

As shown in FIG. 7, the invention includes a number of high permeabilitymetal lines, shown in this embodiment as 702-1 and 702-2. According tothe teachings of the present invention, the number of high permeabilitymetal lines, 702-1 and 702-2, are formed of composite hexaferrite films.As shown in FIG. 7, the number of high permeability metal lines, 702-1and 702-2 are interspaced between the one or more transmission lines,701-1 and 701-2. In one embodiment of the present invention, the one ormore transmission lines, 701-1 and 701-2, and the number or highpermeability metal lines, 702-1 and 702-2, are spaced parallel to oneanother and are oriented lengthwise perpendicular to the plane of thepage illustrated in FIG. 7. As one of ordinary skill in the art willunderstand upon reading this disclosure, any number of transmissionlines, 701-1, . . . , 701-N can be spaced between any number of numberhigh permeability metal lines, 702-1, . . . , 702-N. That is, one ormore high permeability metal lines, 702-1, . . . , 702-N will separateone or more transmission lines, 701-1, . . . , 701-N. In the invention,the one or more transmission lines, 701-1 and 701-2, and the number orhigh permeability metal lines, 702-1 and 702-2, are separated from oneanother and from the pair of electrically conductive planes 704 and 705by an insulator material 706. In one embodiment of the presentinvention, the insulator material 706 includes an oxide.

In one embodiment as shown in FIG. 7, the pair of electricallyconductive planes 704 and 705 each include two layers, 704A, 704B and705A and 705B. In this embodiment, a first layer, 704A and 705Arespectively, include metal ground planes. A second layer or surfacelayer, 704B and 705B respectively, is formed of the same highpermeability material as the number of high permeability metal lines,702-1 and 702-2. That is, the second layer or surface layer, adjacent tothe one or more transmission lines, 701-1 and 701-2, and the number ofhigh permeability metal lines 702-1 and 702-2, are formed of compositehexaferrite films. As one of ordinary skill in the art will understandupon reading the present disclosure, the electrically conductive planes,704 and 705, can be independently coupled to a ground source and/or apower supply bus.

As one of ordinary skill in the art will understand upon reading thisdisclosure, an electrical signal transmitted across the one or moretransmission lines, 701-1 and 701-2 will induce a magnetic fieldsurrounding the one or more transmission lines, 701-1 and 701-2. In theembodiment of FIG. 7 such a magnetic field is illustrated by magneticfield lines 711. According to the teachings of the present invention,the number of high permeability metal lines, 702-1 and 702-2, and theelectrically conductive planes, 704 and 705, provide magnetic shieldingto reduce the amount of magnetically induced noise on neighboringtransmission lines, e.g. 701-1 and 701-2.

As shown in FIG. 7, the second layer or surface layer, adjacent to theone or more transmission lines, 701-1 and 701-2, and the number of highpermeability metal lines 702-1 and 702-2, each formed of compositehexaferrite films, serve to shield the one or more transmission lines,701-1 and 701-2, from such electrically induced magnetic fields. Themagnetic field lines 711 shown in FIG. 7, illustrates the magneticshielding effect provided by the number of high permeability metallines, 702-1 and 702-2, and the second layer or surface layer 704B and705B, from magnetic fields produces by a current transmitted in the oneor more transmission lines, 701-1 and 701-2. As one of ordinary skill inthe art will understand upon reading this disclosure, the first layer,704A and 705A respectively, of the electrically conductive planes, 704and 705, provide a lower resistance such that there is very littleresistance to the path of the return current.

As shown in the embodiment of FIG. 6 and other embodiments below, thesecond layer, or surface layer, 704B and 705B of high permeabilitymetal, e.g. magnetic material composite hexaferrite films, are formed onthe inside of the conductive planes 704 and 705, also referred to as theVss or ground, adjacent to the one or more transmission lines, 701-1 and701-2. However as one of ordinary skill in the art will understand uponreading this disclosure, the second layer, or surface layer, 704B and705B of high permeability metal can also be placed on the outside of theconductive planes 704 and 705. As one of ordinary skill in the art willunderstand upon reading this disclosure, the number of high permeabilitymetal lines 702-1 and 702-2, each formed of composite hexaferrite films,and the second layer, or surface layer, 704B and 705B of highpermeability metal confine the magnetic fields in both the x and ydirection. However, in this embodiment, the one or more transmissionlines, 701-1 and 701-2 are only separated by a high permeabilitymagnetic material that confines the magnetic field on both the x and ydirection.

FIG. 8 illustrates another embodiment for a pair of neighboringtransmission lines, 801-1 and 801-2, according to the teachings of thepresent invention. FIG. 8 illustrates one or more integrated circuitlines, or transmission lines, shown as 801-1 and 801-2. The one or moretransmission lines, 801-1 and 801-2, are spaced between a pair ofelectrically conductive planes 804 and 805. As one of ordinary skill inthe art will understand upon reading this disclosure, any number oftransmission lines, 801-1, . . . , 801-N, can be spaced between theconductive planes 804 and 805. As one of ordinary skill in the art willunderstand upon reading this disclosure, in one embodiment at least oneof the electrically conductive planes is formed on a substrate. As oneof ordinary skill in the art will understand upon reading thisdisclosure, the substrate can include an insulator, a semiconductormaterial, silicon on insulator material, or other materials. Theinvention is not so limited.

As shown in FIG. 8, the invention includes a number of electricallyconductive metal lines, shown in this embodiment as 802-1 and 802-2.According to the teachings of the present invention, the number ofelectrically conductive metal lines, 802-1 and 802-2, include at leastone surface layer 803 formed of a composite hexaferrite film. As shownin the embodiment of FIG. 8, the at least one surface layer 803 formedof a composite hexaferrite film is formed on the number of electricallyconductive metal lines, 802-1 and 802-2, on opposing surfaces of thenumber of electrically conductive lines and adjacent to the number ofintegrated circuit lines, 801-1 and 801-2. As shown in FIG. 8, thenumber of electrically conductive metal lines, 802-1 and 802-2, havingat least one surface layer 803 formed of a composite hexaferrite film,are interspaced between the one or more transmission lines, 801-1 and801-2. In one embodiment of the present invention, the one or moretransmission lines, 801-1 and 801-2, and the number or electricallyconductive metal lines, 802-1 and 802-2, are spaced parallel to oneanother and are oriented lengthwise perpendicular to the plane of thepage illustrated in FIG. 8. As one of ordinary skill in the art willunderstand upon reading this disclosure, any number of transmissionlines, 801-1, . . . , 801-N can be spaced between any number of numberelectrically conductive metal lines, 802-1, . . . , 802-N, having atleast one surface layer 803 formed of a composite hexaferrite film. Thatis, one or more electrically conductive metal lines, 802-1, . . . ,802-N will separate one or more transmission lines, 801-1, . . . ,801-N. In the invention, the one or more transmission lines, 801-1 and801-2, and the number or electrically conductive metal lines, 802-1 and802-2, are separated from one another and from the pair of electricallyconductive planes 804 and 805 by an insulator material 806. In oneembodiment of the present invention, the insulator material 806 includesan oxide.

In one embodiment as shown in FIG. 8, the pair of electricallyconductive planes 804 and 805 each include two layers, 804A, 804B and805A and 805B. In this embodiment, a first layer, 804A and 805Arespectively, include metal ground planes. A second layer or surfacelayer, 804B and 805B respectively, is formed of the same electricallyconductive material as the at least one surface layer 803 on number ofelectrically conductive metal lines, 802-1 and 802-2. That is, thesecond layer or surface layer, adjacent to the one or more transmissionlines, 801-1 and 801-2, and the number of electrically conductive metallines 802-1 and 802-2, are formed of composite hexaferrite films. As oneof ordinary skill in the art will understand upon reading the presentdisclosure, the electrically conductive planes, 804 and 805, can beindependently coupled to a ground source and/or a power supply bus.

As one of ordinary skill in the art will understand upon reading thisdisclosure, an electrical signal transmitted across the one or moretransmission lines, 801-1 and 801-2 will induce a magnetic fieldsurrounding the one or more transmission lines, 801-1 and 801-2. In theembodiment of FIG. 8 such a magnetic field is illustrated by magneticfield lines 811. According to the teachings of the present invention,the number of electrically conductive metal lines, 802-1 and 802-2,having at least one surface layer 803 formed of a composite hexaferritefilm, and the electrically conductive planes, 804 and 805, providemagnetic shielding to reduce the amount of magnetically induced noise onneighboring transmission lines, e.g. 801-1 and 801-2.

As shown in FIG. 8, the second layer or surface layer, adjacent to theone or more transmission lines, 801-1 and 801-2, and the number ofelectrically conductive metal lines 802-1 and 802-2, each formed ofcomposite hexaferrite films, serve to shield the one or moretransmission lines, 801-1 and 801-2, from such electrically inducedmagnetic fields. The magnetic field lines 811 shown in FIG. 8,illustrates the magnetic shielding effect provided by the number ofelectrically conductive metal lines, 802-1 and 802-2, having at leastone surface layer 803 formed of a composite hexaferrite film, and thesecond layer or surface layer 804B and 805B, from magnetic fieldsproduces by a current transmitted in the one or more transmission lines,801-1 and 801-2. As one of ordinary skill in the art will understandupon reading this disclosure, the first layer, 804A and 805Arespectively, of the electrically conductive planes, 804 and 805,provide a lower resistance such that there is very little resistance tothe path of the return current. As one of ordinary skill in the art willunderstand upon reading this disclosure, FIG. 8 shows a similararrangement to that of FIG. 7 but both the electric and magnetic fieldsare now confined in both the x and y direction. Here the conductors areseparated by not only a high permeability magnetic material but asandwich of both a very low resistive ground plane which acts as a lowresistive return path for induced currents (which is shown grounded) andhigh permeability magnetic material.

FIG. 9 illustrates another embodiment for neighboring transmissionlines, 901-1 and 901-2, according to the teachings of the presentinvention. FIG. 9 illustrates one or more integrated circuit lines, ortransmission lines, shown as 901-1 and 901-2. The one or moretransmission lines, 901-1 and 901-2, are spaced between a pair ofelectrically conductive planes 904 and 905. As one of ordinary skill inthe art will understand upon reading this disclosure, any number oftransmission lines, 901-1, . . . , 901-N, can be spaced between theconductive planes 904 and 905. As one of ordinary skill in the art willunderstand upon reading this disclosure, in one embodiment at least oneof the electrically conductive planes is formed on a substrate. As oneof ordinary skill in the art will understand upon reading thisdisclosure, the substrate can include an insulator, a semiconductormaterial, silicon on insulator material, or other materials. Theinvention is not so limited.

As shown in FIG. 9, the invention includes a number of electricallyconductive metal lines, shown in this embodiment as 902-1 and 902-2.According to the teachings of the present invention, the one or moretransmission lines, 901-1 and 901-2, include at least one surface layer915 formed of a composite hexaferrite film. As shown in the embodimentof FIG. 9, the at least one surface layer 915 of a composite hexaferritefilm is formed on the one or more transmission lines, 901-1 and 901-2,on at least three sides of the number of transmission lines, 901-1 and901-2. In this embodiment, the three sides include opposing surfacesadjacent to the number of electrically conductive lines, 902-1 and902-2, and on a side adjacent to the first conductive plane 904. Asshown in FIG. 9, the one or more transmission lines, 901-1 and 901-2,having at least one surface layer 915 formed of a composite hexaferritefilm, are interspaced between the number or electrically conductivemetal lines, 902-1 and 902-2. In one embodiment of the presentinvention, the one or more transmission lines, 901-1 and 901-2, and thenumber or electrically conductive metal lines, 902-1 and 902-2, arespaced parallel to one another and are oriented lengthwise perpendicularto the plane of the page illustrated in FIG. 9. As one of ordinary skillin the art will understand upon reading this disclosure, any number oftransmission lines, 901-1, . . . , 901-N, having at least one surfacelayer 915 formed of a composite hexaferrite film, can be spaced betweenany number of number electrically conductive metal lines, 902-1, . . . ,902-N. That is, one or more electrically conductive metal lines, 902-1,. . . , 902-N will separate one or more transmission lines, 901-1, . . ., 901-N. In the invention, the one or more transmission lines, 901-1 and901-2, and the number or electrically conductive metal lines, 902-1 and902-2, are separated from one another and from the pair of electricallyconductive planes 904 and 905 by an insulator material 906. In oneembodiment of the present invention, the insulator material 906 includesan oxide.

In one embodiment as shown in FIG. 9, the at least one of the pair ofelectrically conductive planes 904 and 905 includes two layers. In theembodiment shown in FIG. 9, conductive plane 905 includes two layers,905A and 905B. In this embodiment, conductive plane 904, and a firstlayer 905A for conductive plane 905, include metal ground planes. Inconductive plane 905 a second layer or surface layer 905B, is formed ofthe same high permeability material as the at least one surface layer915 on the one or more transmission lines, 901-1 and 901-2. That is, thesecond layer or surface layer, 905B adjacent to the one or moretransmission lines, 901-1 and 901-2, and the number of electricallyconductive metal lines 902-1 and 902-2, are formed of compositehexaferrite films. As one of ordinary skill in the art will understandupon reading the present disclosure, the electrically conductive planes,904 and 905, can be independently coupled to a ground source and/or apower supply bus.

As one of ordinary skill in the art will understand upon reading thisdisclosure, an electrical signal transmitted across the one or moretransmission lines, 901-1 and 901-2 will induce a magnetic fieldsurrounding the one or more transmission lines, 901-1 and 901-2. In theembodiment of FIG. 9 such a magnetic field is illustrated by magneticfield lines 911. According to the teachings of the present invention,the one or more transmission lines, 901-1 and 901-2, having at least onesurface layer 915 formed of a composite hexaferrite film, the number ofelectrically conductive metal lines 902-1 and 902-2, and theelectrically conductive planes, 904 and 905, provide magnetic shieldingto reduce the amount of magnetically induced noise on neighboringtransmission lines, e.g. 901-1 and 901-2.

As shown in FIG. 9, the second layer or surface layer 905B, adjacent tothe one or more transmission lines, 901-1 and 901-2, having at least onesurface layer 915 formed of a composite hexaferrite film, theelectrically conductive planes, 904 and 905, and the number ofelectrically conductive metal lines 902-1 and 902-2, serve to shield theone or more transmission lines, 901-1 and 901-2, from such electricallyinduced magnetic fields. The magnetic field lines 911 shown in FIG. 9,illustrates the magnetic shielding effect provided by the one or moretransmission lines, 901-1 and 901-2, having at least one surface layer915 formed of a composite hexaferrite film, the number of electricallyconductive metal lines 902-1 and 902-2 and the second layer or surfacelayer 905B, from magnetic fields produced by a current transmitted inthe one or more transmission lines, 901-1 and 901-2. As one of ordinaryskill in the art will understand upon reading this disclosure,conductive plane and the first layer 905A, of the electricallyconductive planes, 904 and 905, provide a lower resistance such thatthere is very little resistance to the path of the return current.

The embodiment provided by FIG. 9 is easy to manufacture. Here thecurrent carrying low resistive conductors or metal lines, 901-1 and901-2, are encased on three sides by a high permeability magneticmaterial and separated from one another by low resistive metal linesthat are grounded. To provide magnetic field confinement in the Ydirection, a sandwich layer is used at the top of the conductors, 901-1and 901-2, as part of conductive plane 905. This sandwich layer iscomposed of both a low resistive component 905A as well as a highpermeability component 905B. The bottom side of the embedded metal linesor conductors, 901-1 and 901-2, contain only a ground plane 904. Thisembodiment provides complete electric and magnetic field confinement.

FIG. 10 illustrates another embodiment for neighboring transmissionlines, 1001-1 and 1001-2, according to the teachings of the presentinvention. FIG. 10 illustrates one or more integrated circuit lines, ortransmission lines, shown as 1001-1 and 1001-2. The one or moretransmission lines, 1001-1 and 1001-2, are spaced between a pair ofelectrically conductive planes 1004 and 1005. As one of ordinary skillin the art will understand upon reading this disclosure, any number oftransmission lines, 1001-1, . . . , 1001-N, can be spaced between theconductive planes 1004 and 1005. As one of ordinary skill in the artwill understand upon reading this disclosure, in one embodiment at leastone of the electrically conductive planes is formed on a substrate. Asone of ordinary skill in the art will understand upon reading thisdisclosure, the substrate can include an insulator, a semiconductormaterial, silicon on insulator material, or other materials. Theinvention is not so limited.

As shown in FIG. 10, the invention includes a number of electricallyconductive metal lines, shown in this embodiment as 1002-1 and 1002-2.According to the teachings of the present invention, the number ofelectrically conductive metal lines, 1002-1 and 1002-2, include at leastone surface layer 1003 formed of a composite hexaferrite film. As shownin the embodiment of FIG. 10, the at least one surface layer 1003 of acomposite hexaferrite film is formed on the number of electricallyconductive metal lines, 1002-1 and 1002-2, on at least three sides ofthe number of electrically conductive metal lines, 1002-1 and 1002-2. Inthis embodiment, the three sides include opposing surfaces adjacent tothe one or more transmission lines, 1001-1 and 1001-2, and on a sideadjacent to the first conductive plane 1004. As shown in FIG. 10, thenumber of electrically conductive metal lines, 1002-1 and 1002-2, havingat least one surface layer 1015 formed of a composite hexaferrite film,are interspaced between the one or more transmission lines, 1001-1 and1001-2. Further, in this embodiment, the one or more transmission lines,1001-1 and 1001-2, include at least one surface layer 1015 formed of acomposite hexaferrite film. As shown in the embodiment of FIG. 10, theat least one surface layer 1015 of a composite hexaferrite film isformed on the one or more transmission lines, 1001-1 and 1001-2, on atleast three sides of the number of transmission lines, 1001-1 and1001-2. In this embodiment, the three sides include opposing surfacesadjacent to the number of electrically conductive lines, 1002-1 and1002-2, and on a side adjacent to the first conductive plane 1004. Asshown in FIG. 10, the one or more transmission lines, 1001-1 and 1001-2,having at least one surface layer 1015 formed of a composite hexaferritefilm, are interspaced between the number or electrically conductivemetal lines, 1002-1 and 1002-2 also having at least one surface layer1003 formed of a composite hexaferrite film. In one embodiment of thepresent invention, the one or more transmission lines, 1001-1 and1001-2, and the number or electrically conductive metal lines, 1002-1and 1002-2, are spaced parallel to one another and are orientedlengthwise perpendicular to the plane of the page illustrated in FIG.10. As one of ordinary skill in the art will understand upon readingthis disclosure, any number of transmission lines, 1001-1, . . . ,1001-N, having at least one surface layer 1003 formed of a compositehexaferrite film, can be spaced between any number of numberelectrically conductive metal lines, 1002-1, . . . , 1002-N also havingat least one surface layer 1003 formed of a composite hexaferrite film.That is, one or more electrically conductive metal lines, 1002-1, . . ., 1002-N will separate one or more transmission lines, 1001-1, . . . ,1001-N. In the invention, the one or more transmission lines, 1001-1 and1001-2, and the number or electrically conductive metal lines, 1002-1and 1002-2, are separated from one another and from the pair ofelectrically conductive planes 1004 and 1005 by an insulator material1006. In one embodiment of the present invention, the insulator material1006 includes an oxide.

In one embodiment as shown in FIG. 10, the at least one of the pair ofelectrically conductive planes 1004 and 1005 includes two layers. In theembodiment shown in FIG. 10, conductive plane 1005 includes two layers,1005A and 1005B. In this embodiment, conductive plane 1004, and a firstlayer 1005A for conductive plane 1005, include metal ground planes. Inconductive plane 1005 a second layer or surface layer 1005B, is formedof the same high permeability material as the at least one surface layer1015 on the one or more transmission lines, 1001-1 and 1001-2 and the atleast one surface layer 1003 formed on the number or electricallyconductive metal lines, 1002-1 and 1002-2. That is, the second layer orsurface layer, 1005B adjacent to the one or more transmission lines,1001-1 and 1001-2, and the number of electrically conductive metal lines1002-1 and 1002-2, are formed of composite hexaferrite films. As one ofordinary skill in the art will understand upon reading the presentdisclosure, the electrically conductive planes, 1004 and 1005, can beindependently coupled to a ground source and/or a power supply bus.

As one of ordinary skill in the art will understand upon reading thisdisclosure, an electrical signal transmitted across the one or moretransmission lines, 1001-1 and 1001-2 will induce a magnetic fieldsurrounding the one or more transmission lines, 1001-1 and 1001-2. Inthe embodiment of FIG. 10 such a magnetic field is illustrated bymagnetic field lines 1011. According to the teachings of the presentinvention, the one or more transmission lines, 1001-1 and 1001-2, havingat least one surface layer 1015 formed of a composite hexaferrite film,the number of electrically conductive metal lines 1002-1 and 1002-2 alsohaving at least one surface layer 1003 formed of a composite hexaferritefilm, and the electrically conductive planes, 1004 and 1005, providemagnetic shielding to reduce the amount of magnetically induced noise onneighboring transmission lines, e.g. 1001-1 and 1001-2.

As shown in FIG. 10, the second layer or surface layer 1005B, adjacentto the one or more transmission lines, 1001-1 and 1001-2, having atleast one surface layer 1015 formed of a composite hexaferrite film, theelectrically conductive planes, 1004 and 1005, and the number ofelectrically conductive metal lines 1002-1 and 1002-2 also having atleast one surface layer 1003 formed of a composite hexaferrite film,serve to shield the one or more transmission lines, 1001-1 and 1001-2,from such electrically induced magnetic fields. The magnetic field lines1011 shown in FIG. 10, illustrates the magnetic shielding effectprovided by the one or more transmission lines, 1001-1 and 1001-2,having at least one surface layer 1015 formed of a composite hexaferritefilm, the number of electrically conductive metal lines 1002-1 and1002-2 also having at least one surface layer 1003 formed of a compositehexaferrite film, and the second layer or surface layer 1005B, frommagnetic fields produced by a current transmitted in the one or moretransmission lines, 1001-1 and 1001-2. As one of ordinary skill in theart will understand upon reading this disclosure, conductive plane andthe first layer 1005A, of the electrically conductive planes, 1004 and1005, provide a lower resistance such that there is very littleresistance to the path of the return current.

FIG. 10 is another embodiment that is very easy to manufacture. The maindifference in this case being that the electrically conductive metallines, 1002-1 and 1002-2, which were previously used only for electricfield confinement in the embodiment of FIG. 9 can also be used formagnetic field confinement. An alternate configuration to that shown inFIG. 10 is shown in FIG. 12. In the embodiment of FIG. 12, as describedin more detail below, the one or more transmission lines, 1001-1 and1001-2 do not have a magnetic material around them.

FIG. 11 illustrates another embodiment for neighboring transmissionlines, 1101-1 and 1101-2, according to the teachings of the presentinvention. FIG. 11 illustrates one or more integrated circuit lines, ortransmission lines, shown as 1101-1 and 1101-2. The one or moretransmission lines, 1101-1 and 1101-2, are spaced between a pair ofelectrically conductive planes 1104 and 1105. As one of ordinary skillin the art will understand upon reading this disclosure, any number oftransmission lines, 1101-1, . . . , 1101-N, can be spaced between theconductive planes 1104 and 1105. As one of ordinary skill in the artwill understand upon reading this disclosure, in one embodiment at leastone of the electrically conductive planes is formed on a substrate. Asone of ordinary skill in the art will understand upon reading thisdisclosure, the substrate can include an insulator, a semiconductormaterial, silicon on insulator material, or other materials. Theinvention is not so limited.

As shown in FIG. 11, the invention includes a number of highpermeability metal lines, shown in this embodiment as 1102-1 and 1102-2.According to the teachings of the present invention, the number of highpermeability metal lines, 1102-1 and 1102-2, are formed of compositehexaferrite films. As shown in FIG. 11, the number of high permeabilitymetal lines, 1102-1 and 1102-2 are interspaced between the one or moretransmission lines, 1101-1 and 1101-2. In one embodiment of the presentinvention, the one or more transmission lines, 1101-1 and 1101-2, andthe number or high permeability metal lines, 1102-1 and 1102-2, arespaced parallel to one another and are oriented lengthwise perpendicularto the plane of the page illustrated in FIG. 11. Further, in thisembodiment, the one or more transmission lines, 1101-1 and 1101-2,include at least one surface layer 1115 formed of a compositehexaferrite film. As shown in the embodiment of FIG. 11, the at leastone surface layer 1115 of a composite hexaferrite film is formed on theone or more transmission lines, 1101-1 and 1101-2, on two sides of thenumber of transmission lines, 1101-1 and 1101-2. In this embodiment, thetwo sides include opposing surfaces adjacent to the first and the secondconductive planes 1104 and 1105. As shown in FIG. 11, the one or moretransmission lines, 1101-1 and 1101-2, having at least one surface layer1115 formed of a composite hexaferrite film, are interspaced between thenumber high permeability metal lines, 1102-1 and 1102-2. In oneembodiment of the present invention, the one or more transmission lines,1101-1 and 1101-2, and the number or high permeability metal lines,1102-1 and 1102-2, are spaced parallel to one another and are orientedlengthwise perpendicular to the plane of the page illustrated in FIG.11. As one of ordinary skill in the art will understand upon readingthis disclosure, any number of transmission lines, 1101-1, . . . ,1101-N, having at least one surface layer 1115 formed of a compositehexaferrite film, can be spaced between any number of number highpermeability metal lines, 1102-1, . . . , 1102-N. That is, one or morehigh permeability metal lines, 1102-1, . . . , 1102-N will separate oneor more transmission lines, 1001-1, . . . , 1101-N. In the invention,the one or more transmission lines, 1101-1 and 1101-2, and the number orhigh permeability metal lines, 1102-1 and 1102-2, are separated from oneanother and from the pair of electrically conductive planes 1104 and1105 by an insulator material 1106. In one embodiment of the presentinvention, the insulator material 1106 includes an oxide. In analternative embodiment, the one or more transmission lines, 1101-1 and1101-2, and the number or high permeability metal lines, 1102-1 and1102-2, do not have to be located between the pair of electricallyconductive planes 1104 and 1105, but are still encapsulated by aninsulator material 1106. As one of ordinary skill in the art willunderstand upon reading the present disclosure, the high permeabilityplanes, 1104 and 1105, can be independently coupled to a ground sourceand/or a power supply bus.

As one of ordinary skill in the art will understand upon reading thisdisclosure, an electrical signal transmitted across the one or moretransmission lines, 1101-1 and 1101-2 will induce a magnetic fieldsurrounding the one or more transmission lines, 1101-1 and 1101-2. Inthe embodiment of FIG. 11 such a magnetic field is illustrated bymagnetic field lines 1112. According to the teachings of the presentinvention, the one or more transmission lines, 1101-1 and 1101-2, havingat least one surface layer 1115 formed of a composite hexaferrite film,the number of high permeability metal lines 1102-1 and 1102-2, and theelectrically conductive planes, 1104 and 1105, provide magneticshielding to reduce the amount of magnetically induced noise onneighboring transmission lines, e.g. 1101-1 and 1101-2.

As shown in FIG. 11, the one or more transmission lines, 1101-1 and1101-2, having at least one surface layer 1115 formed of a compositehexaferrite film, the electrically conductive planes, 1104 and 1105, andthe number of high permeability metal lines 1102-1 and 1102-2, serve toshield the one or more transmission lines, 1101-1 and 1101-2, from suchelectrically induced magnetic fields. The magnetic field lines 1111shown in FIG. 11, illustrates the magnetic shielding effect provided bythe one or more transmission lines, 1101-1 and 1101-2, having at leastone surface layer 1115 formed of a composite hexaferrite film, and thenumber of high permeability metal lines 1102-1 and 1102-2, from magneticfields produced by a current transmitted in the one or more transmissionlines, 1101-1 and 1101-2. As one of ordinary skill in the art willunderstand upon reading this disclosure, the electrically conductiveplanes, 1104 and 1105, provide a lower resistance such that there isvery little resistance to the path of the return current. FIG. 11 isanother possibility that provides for magnetic confinement in alldirections, but in this case, the magnetic material is only placed atthe top and bottom of the one or more transmission lines, 1101-1 and1101-2. The one or more transmission lines, 1101-1 and 1101-2 areseparated by a high permeability magnetic material, e.g. the number ofhigh permeability metal lines 1102-1 and 1102-2. In the embodiment ofFIG. 11 the electrically conductive planes 1104 and 1105 encloses theone or more transmission lines, 1101-1 and 1101-2 with low resistivemetals on both sides.

FIG. 12 illustrates another embodiment for neighboring transmissionlines, 1201-1 and 1201-2, according to the teachings of the presentinvention. FIG. 12 illustrates one or more integrated circuit lines, ortransmission lines, shown as 1201-1 and 1201-2. The one or moretransmission lines, 1201-1 and 1201-2, are spaced between a pair ofelectrically conductive planes 1204 and 1205. As one of ordinary skillin the art will understand upon reading this disclosure, any number oftransmission lines, 1201-1, . . . , 1201-N, can be spaced between theconductive planes 1204 and 1205. As one of ordinary skill in the artwill understand upon reading this disclosure, in one embodiment at leastone of the electrically conductive planes is formed on a substrate. Asone of ordinary skill in the art will understand upon reading thisdisclosure, the substrate can include an insulator, a semiconductormaterial, silicon on insulator material, or other materials. Theinvention is not so limited.

As shown in FIG. 12, the invention includes a number of electricallyconductive metal lines, shown in this embodiment as 1202-1 and 1202-2.According to the teachings of the present invention, the number ofelectrically conductive metal lines, 1202-1 and 1202-2, include at leastone surface layer 1203 formed of a composite hexaferrite film. As shownin the embodiment of FIG. 12, the at least one surface layer 1203 of acomposite hexaferrite film is formed on the number of electricallyconductive metal lines, 1202-1 and 1202-2, on at least three sides ofthe number of electrically conductive metal lines, 1202-1 and 1202-2. Inthis embodiment, the three sides include opposing surfaces adjacent tothe one or more transmission lines, 1201-1 and 1201-2, and on a sideadjacent to the first conductive plane 1204. As shown in FIG. 12, thenumber of electrically conductive metal lines, 1202-1 and 1202-2, havingat least one surface layer 1203 formed of a composite hexaferrite film,are interspaced between the one or more transmission lines, 1201-1 and1201-2. As shown in FIG. 12, the one or more transmission lines, 1201-1and 1201-2 are interspaced between the number or electrically conductivemetal lines, 1202-1 and 1202-2 having at least one surface layer 1203formed of a composite hexaferrite film. In one embodiment of the presentinvention, the one or more transmission lines, 1201-1 and 1201-2, andthe number or electrically conductive metal lines, 1202-1 and 1202-2,are spaced parallel to one another and are oriented lengthwiseperpendicular to the plane of the page illustrated in FIG. 12. As one ofordinary skill in the art will understand upon reading this disclosure,any number of transmission lines, 1201-1, . . . , 1201-N, can be spacedbetween any number of number electrically conductive metal lines,1202-1, . . . , 1202-N having at least one surface layer 1203 formed ofa composite hexaferrite film. That is, one or more electricallyconductive metal lines, 1202-1, . . . , 1202-N will separate one or moretransmission lines, 1201-1, . . . , 1201-N. In the invention, the one ormore transmission lines, 1201-1 and 1201-2, and the number orelectrically conductive metal lines, 1202-1 and 1202-2, are separatedfrom one another and from the pair of electrically conductive planes1204 and 1205 by an insulator material 1206. In one embodiment of thepresent invention, the insulator material 1206 includes an oxide.

In one embodiment as shown in FIG. 12, the pair of electricallyconductive planes 1204 and 1205 each include two layers, 1204A, 1204Band 1205A and 1205B. In this embodiment, a first layer, 1204A and 1205Arespectively, include metal ground planes. A second layer or surfacelayer, 1204B and 1205B respectively, is formed of the same electricallyconductive material as the at least one surface layer 1203 on number ofelectrically conductive metal lines, 1202-1 and 1202-2. That is, thesecond layer or surface layer, adjacent to the one or more transmissionlines, 1201-1 and 1201-2, and the at least one surface layer 1203 on thenumber of electrically conductive metal lines 1202-1 and 1202-2, areformed of composite hexaferrite films. As one of ordinary skill in theart will understand upon reading the present disclosure, theelectrically conductive planes, 1204 and 1205, can be independentlycoupled to a ground source and/or a power supply bus.

As one of ordinary skill in the art will understand upon reading thisdisclosure, an electrical signal transmitted across the one or moretransmission lines, 1201-1 and 1201-2 will induce a magnetic fieldsurrounding the one or more transmission lines, 1201-1 and 1201-2. Inthe embodiment of FIG. 12 such a magnetic field is illustrated bymagnetic field lines 1211. According to the teachings of the presentinvention, the one or more transmission lines, 1201-1 and 1201-2, thenumber of electrically conductive metal lines 1202-1 and 1202-2 havingat least one surface layer 1203 formed of a composite hexaferrite film,and the electrically conductive planes, 1204 and 1205, provide magneticshielding to reduce the amount of magnetically induced noise onneighboring transmission lines, e.g. 1201-1 and 1201-2.

As shown in FIG. 12, the second layer or surface layer 1204B and 1205B,adjacent to the one or more transmission lines, 1201-1 and 1201-2 andthe number of electrically conductive metal lines 1202-1 and 1202-2having at least one surface layer 1203 formed of a composite hexaferritefilm, serve to shield the one or more transmission lines, 1201-1 and1201-2, from such electrically induced magnetic fields. The magneticfield lines 1211 shown in FIG. 12, illustrate the magnetic shieldingeffect provided by the number of electrically conductive metal lines1202-1 and 1202-2 having at least one surface layer 1203 formed of acomposite hexaferrite film, and the second layer or surface layer 1204Band 1205B, from magnetic fields produced by a current transmitted in theone or more transmission lines, 1201-1 and 1201-2. As one of ordinaryskill in the art will understand upon reading this disclosure, the firstlayers 1204A and 1205A, of the electrically conductive planes, 1204 and1205, provide a lower resistance such that there is very littleresistance to the path of the return current. FIG. 12 highlights aconfiguration that is similar to FIG. 10 but allows for more space to beused for the one or more transmission lines, 1201-1 and 1201-2 sincethey are not encased on magnetic material.

FIG. 13 is a block diagram which illustrates an embodiment of a system1300 using line signaling according to teachings of the presentinvention. The system 1300 includes a low output impedance driver 1310having a driver impedance, as is well known in the art. The low outputimpedance driver 1310 is coupled to a transmission line circuit 1320.Embodiments of the transmission line circuit 1320 are described andpresented above with reference to FIGS. 6-12. Moreover, the system 1300includes a termination circuit 1330 having a termination impedance thatis matched to the impedance of the transmission line circuit 1320.

FIG. 14 is a block diagram which illustrates an embodiment of a system1400 according to teaching of the present invention. The system 1400includes an integrated circuit 1410. The integrated circuit 1410includes the transmission line circuit described and presented abovewith reference to FIGS. 6-12. Additionally, the system 1400 includes aprocessor 1420 that is operatively coupled to the integrated circuit1410. The processor 1420 is coupled to the integrated circuit 1410through a system bus 1430. In one embodiment, the processor 1420 and theintegrated circuit 1410 are on the same semiconductor chip.

Composite Hexaferrite Films

Recently, multiple layer chip inductors applied in the hyperfrequencyregions have been rapidly developed as surface mounting devices.Multilayer chip inductors are produced by coating ferrites and internalelectrode pastes alternately and then coating. Because multilayertechnology has become mature, the properties of multilayer chipinductors largely depend on the electromagnetic properties of thelow-temperature sintered ferrites. Much work has focused on the NiZnsystem ferrite applied in medium to high-frequency regions, 1<300 MHz.As for hyperfrequency regions (300<1000 MHz), no ideal material has beenadopted so far.

Co₂Z ferrite with planar structure is considered to be a candidatematerial for multilayer chip inductors because of its high initialpermeability and its high Curie temperature. Especially its high cutofffrequency of 3 GHz (much higher than that of 300 MHz for spinel ferries)brings it into the hyperfrequency region useful for chip inductor andcommunication components. (See generally, H. G. Zhang, J. Zhou, HighTechnol. Lett (Chin), 10, (115), 96-97, 2000; and H. M. Song, C. J.Chen, H. C. Lin, IEEE Trans, Magn., 30, (6), 4875-4878, 1994). From thecrystallographic point of view, Z-type hexaferrites are among the mostcomplex compounds in the family of hexaferrites with planar hexagonalstructure. The unit cell of a z-type hexaferrite contain 140 atoms, andbelongs to the P6₃/mmc space group. Metal ions (Fe³⁺ and Co²⁺), however,are located in nonequivalent interstitial sites. Theoretically, thehexaferrite can be treated as a sum of two simpler hexaferrites, namelyof M (BaFe₁₂O₁₉) and Y (Ba₂Co₂Fe₁₂O₂₂) types. (See generally, HongguoZhang, et al., “Investigation on structure and properties oflow-temperature sintered composite ferrites”, Materials ResearchBulletin, 35, 2207-2215, 2001).

In the present invention, the method disclosed in the above article byZhang and et al. is followed in choosing different compositions of thecomposite ferrite system(1−x)Ba₃Co₂Fe₂₄O₄₁+x(Ni_(0.06)Zn_(0.20)Cu_(0.20))Fe₂O₄+0.5 wt % Bi₂O₃,where x=0.1 and 0.2. According to the article by Zhang, an attempt wasmade both to promote formation of the dense composite ferrite at a lowtemperature and to improve the microstructure and properties of thesintered materials. Therein a 0.5 wt % Bi₂O₃ dopant was taken as a fixedexperimental variables, and was used to lower the sintering temperature,prevent (Ni_(0.60)Zn_(0.20)Cu_(0.20))Fe₂O₄ from agglomeration on thegrain boundaries, suppress abnormal grain growth, and hinder(Ni_(0.60)Zn_(0.20)Cu_(0.20))Fe₂O₄ migration or diffusion into Co₂Zgrains.

The experimental powders of (Ni_(0.60)Zn_(0.20)Cu_(0.20))Fe₂O₄ and Co₂Zferrites were synthesized by the gel self-propagating method. Based onsol-gel technique, ultrafine and highly reactive powders were obtainedand then utilized to synthesize composite ferrites. The method couldmake the dry blend-homogeneous organic matter propagate for a few hoursafter igniting. The ignited residual contained a stoichiometric amountof cations, and could be used to synthesize various pure ferrite withoutcalcining powders.

The powders were mixed in a ball mill for 4 hours. The mixed powderswere then pressed in a stainless steel die under a pressure of about40,000 N/m₂ ² with 5 wt % PVA as lubricant. The pressed pellets andsamples sintered in air for 4 hours and cooled in the furnace. Aftereach sintering experiment, the weights and dimensions of the sample weremeasured at room temperature to determine bulk densities. An HP4191Aimpedance analyzer was used to measure the frequency range of 1-1000MHz.

Samples with the composition x=0.10 and 0.15 presented hyperfrequencyproperties at low sintering temperatures: an initial permeability of5.5, a quality factor of more than 20, and a cutoff frequency of above 2GHz. Moreover, the electrical resistivity was 2×10⁷ ohm-cm, and thedielectric constant was about 15. All these meet an importantrequirement for fabrication of multilayer chip inductors.

Although multiple layer inductors can be produced by coating ferritepastes or other coating techniques, they can be alternatively bedeposited using sputtering techniques which can be better suited for ICfabrication processing. In this case a sputtering target can be usedthat results in the deposition of the final film composition being thatof the desired composition. As different elements of the sputteringtarget have different sputter rates, it should be noted that thecomposition of the sputtering target does not necessary have to be ofthe same composition as the final film. For example in order to deposita film of Co₂Z(Ba₃Co₂Fe₂₄O₄₁) or (Ni_(0.60)Zn_(0.20)Cu_(0.20))Fe₂O₄, asputtering target can be used that has all the elements in it but notnecessarily in that exact ratio. One advantage of using sputteringtechniques is the lower and shorter temperature durations that might berequired instead of the conventional sintering approaches. For example,rapid thermal annealing (RTA) can be done after sputtering to anneal andsinter films. Anneal temperature are dependent on the thickness andcomposition of the films and can vary from 500 to 1000 degrees Celsius.Further the use of sputtering or evaporation techniques whether donewith a single or a multitude of targets can achieve the structuralgeometries and cross-section shown in the embodiments of FIGS. 6-12.Although the use of sputtering techniques can be expensive fordepositing material with more than two or three elements it can be costcompetitive for three or fewer elements. The process techniques andmaterials described in this section represent typical materials, howeveralternative materials and thin film processing compatible for waferprocessing can be employed.

Any technique which can or has been used to produce multilayer inductorswith films of high permeability magnetic particles can be adapted toproducing films for magnetic shielding according to the teachings of thepresent invention.

Conclusion

Thus, structures and methods are provided for improved, high speedtransmission lines on integrated circuits. High speed interconnectionsare provided which accord exemplary performance. That is, the inventiondescribed here provides an improved and efficiently fabricated techniquefor high speed transmission lines on CMOS integrated circuits. Inaddition, the novel low input impedance CMOS circuit offers thefollowing advantages: (1) the signal delay depends only on the velocityof light on the line and is easily predictable and reproducible,eliminating or allowing for compensation for signal and/or clock skew,(2) there are no reflections at the receiving end of the line and thisminimizes ringing, and (3) noise signals will be smaller due to weakercoupling between lines resulting in better signal to noise ratios, thenoise current will only be a small fraction of the signal current.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement which is calculated to achieve the same purpose maybe substituted for the specific embodiment shown. This application isintended to cover any adaptations or variations of the presentinvention. It is to be understood that the above description is intendedto be illustrative, and not restrictive. Combinations of the aboveembodiments, and other embodiments will be apparent to those of skill inthe art upon reviewing the above description. The scope of the inventionincludes any other applications in which the above structures andfabrication methods are used. The scope of the invention should bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

What is claimed is:
 1. A method for forming transmission lines in anintegrated circuit, comprising: forming a first layer of electricallyconductive material on a substrate; forming a first layer of insulatingmaterial on the first layer of the electrically conductive material;forming a pair of high permeability metal lines on the first layer ofinsulating material, wherein the pair of high permeability metal linesinclude composite ferrite films; forming a transmission line on thefirst layer of insulating material interposed between and parallel withthe pair of high permeability metal lines; forming a second layer ofinsulating material on the transmission line and the pair of highpermeability metal lines; and forming a second layer of electricallyconductive material on the second layer of insulating material.
 2. Themethod of claim 1, wherein forming the first and second layer ofinsulating material includes forming an oxide layer.
 3. The method ofclaim 1, wherein forming the second layer of insulating materialincludes forming the second layer of insulating material with athickness which is at least approximately 50% greater than a thicknessof the transmission line and the pair of electrically conductive lines.4. The method of claim 1, further comprising coupling the second layerof electrically conductive material to a power supply.
 5. The method ofclaim 1, wherein forming the first layer of insulating material includesforming the first layer of insulating material by chemical vapordeposition (CVD).
 6. The method of claim 1, wherein forming the firstlayer of electrically conductive material on the substrate includesforming the first layer of electrically conductive material on a SOI(Silicon On Insulator) material.
 7. The method of claim 1, wherein themethod further includes forming a composite hexaferrite as the compositeferrite of each high permeability metal line.
 8. The method of claim 1,wherein the method further includes forming a composite hexaferritecontaining (1−x)Ba₃Co₂Fe₂₄O₄₁+x(Ni_(0.60)Zn_(0.20)Cu_(0.20))Fe₂O₂O₄+0.5wt % Bi₂O₃ with x substantially equal to 0.1 as the composite ferrite ofeach high permeability metal line.
 9. The method of claim 1, wherein themethod further includes forming a composite hexaferrite containing(1−x)Ba₃Co₂Fe₂₄O₄₁+x(Ni_(0.60)Zn_(0.20)Cu_(0.20))Fe₂O₄+0.5 wt % Bi₂O₃with x substantially equal to 0.2 as the composite ferrite of each highpermeability metal line.
 10. The method of claim 1, wherein the methodfurther includes forming a number of transmission lines interposed amongand parallel with a number of high permeability metal lines.
 11. Amethod for forming transmission lines in an integrated circuit,comprising: forming a first conductive plane on a substrate; forming alayer of insulating material on the first conductive plane; forming apair of magnetic metal lines in the layer of insulating material, eachmagnetic metal line formed containing a ferrite; forming a transmissionline in the layer of insulating material, the transmission lineinterposed between and parallel with the pair of magnetic metal lines;and forming a second conductive plane on the layer of insulatingmaterial, wherein forming at least one of the first and secondconductive planes includes forming two layers, one layer as a conductivelayer and the other layer as a plane of magnetic material.
 12. Themethod of claim 11, wherein the method further includes forming acomposite ferrite as the ferrite of each magnetic metal line.
 13. Themethod of claim 11, wherein the method further includes forming a Co₂Zferrite as the ferrite of each magnetic metal line.
 14. The method ofclaim 11, wherein the method further includes forming a compositehexaferrite as the ferrite of each magnetic metal line.
 15. The methodof claim 11, wherein the method further includes forming a compositehexaferrite containing(1−x)Ba₃Co₂Fe₂₄O₄₁+x(Ni_(0.60)Zn_(0.20)Cu_(0.20))Fe₂O₄+0.5 wt % Bi₂O₃with x substantially equal to 0.1 as the ferrite of each magnetic metalline.
 16. The method of claim 11, wherein the method further includesforming a composite hexaferrite containing(1−x)Ba₃Co₂Fe₂₄O₄₁+x(Ni_(0.60)Zn_(0.20)Cu_(0.20))Fe₂O₄+0.5 wt % Bi₂O₃with x substantially equal to 0.2 as the ferrite of each magnetic metalline.
 17. The method of claim 11, wherein the method further includesforming a number of transmission lines interposed among and parallelwith a number of magnetic metal lines.
 18. The method of claim 11,wherein forming the layer of insulating material includes forming thelayer of insulating material by chemical vapor deposition (CVD).
 19. Themethod of claim 11, wherein forming two layers, one layer as aconductive layer and the other layer as a plane of magnetic material,includes forming the conductive layer as a metal ground plane andforming the plane of magnetic material as a film containing a compositehexaferrite.
 20. The method of claim 11, wherein forming the first andsecond conductive planes includes forming both the first and the secondconductive plane as two layers, one layer as a conductive layer and theother layer as a plane of magnetic material, the magnetic material beingthe same as for the magnetic metal lines.
 21. The method of claim 11,wherein forming two layers, one layer as a conductive layer and theother layer as a plane of magnetic material, includes forming theconductive layer with a resistance lower than the plane of magneticmaterial.
 22. The method of claim 11, wherein forming two layers, onelayer as a conductive layer and the other layer as a plane of magneticmaterial, includes forming the conductive layer as a metal conductiveplane with the plane of magnetic material closer to the transmissionline than the metal conductive plane.
 23. The method of claim 11,wherein forming two layers, one layer as a conductive layer and theother layer as a plane of magnetic material, includes forming theconductive layer as a metal conductive plane closer to the transmissionline than the plane of magnetic material.
 24. A method for formingtransmission lines in an integrated circuit, comprising: forming a firstconductive plane on a substrate; forming a first layer of insulatingmaterial on the first conductive plane; forming a transmission line onthe first layer of insulating material; forming a pair of conductivemetal lines on the first layer of insulating material with thetransmission line interposed between and parallel with the pair ofconductive metal lines, wherein each conductive metal line has at leastone surface layer formed of a high permeability material containing aferrite encasing the conductive metal line on two opposing sidesparallel to the transmission line; forming a second layer of insulatingmaterial on the transmission line and the pair of conductive metallines; and forming a second conductive plane on the second layer ofinsulating material, wherein forming at least one of the first andsecond conductive planes includes forming two layers, one layer as aconductive layer and the other layer as a plane of high permeabilitymaterial.
 25. The method of claim 24, wherein the method furtherincludes forming a composite hexaferrite as the ferrite of the highpermeability material formed as at least one surface layer of eachconductive metal line.
 26. The method of claim 24, wherein the methodfurther includes forming a Co₂Z ferrite as the ferrite of the highpermeability material formed as at least one surface layer of eachconductive metal line.
 27. The method of claim 24, wherein the methodfurther includes forming a composite hexaferrite containing(1−x)Ba₃Co₂Fe₂₄O₄₁+x(Ni_(0.60)Zn_(0.20)Cu_(0.20))Fe₂O₄+0.5 wt % Bi₂O₃with x substantially equal to 0.1 as the ferrite of the highpermeability material formed as at least one surface layer of eachconductive metal line.
 28. The method of claim 24, wherein the methodfurther includes forming a composite hexaferrite containing(1−x)Ba₃Co₂Fe₂₄O₄₁+x(Ni_(0.60)Zn_(0.20)Cu_(0.20))Fe₂O₄+0.5 wt % Bi₂O₃with x substantially equal to 0.2 as the ferrite of the highpermeability material formed as at least one surface layer of eachconductive metal line.
 29. The method of claim 24, wherein the methodfurther includes forming a number of transmission lines interposed amongand parallel with a number of conductive metal lines, each conductivemetal line having at least one surface layer formed of a highpermeability material encasing the conductive metal line on two opposingsides parallel to the number of transmission lines.
 30. The method ofclaim 24, wherein the method further includes forming the pair ofconductive metal lines coupled to ground.
 31. The method of claim 24,wherein forming two layers, one layer as a conductive layer and theother layer as a plane of high permeability material includes formingthe conductive layer as a metal ground plane and forming the plane ofhigh permeability material as a film containing a composite hexaferrite.32. The method of claim 24, wherein forming the first and secondconductive planes includes forming both the first and the secondconductive plane as two layers, one layer as a conductive layer and theother layer as a plane of high permeability material, the highpermeability material being the same as the high permeability materialof the conductive metal lines.
 33. The method of claim 24, whereinforming two layers, one layer as a conductive layer and the other layeras a plane of high permeability material, includes forming theconductive layer with a resistance lower than the plane of highpermeability material.
 34. The method of claim 24, wherein forming twolayers, one layer as a conductive layer and the other layer as a planeof high permeability material, includes forming the conductive layer asa metal conductive plane with the plane of high permeability materialcloser to the transmission line than the metal conductive plane.
 35. Themethod of claim 24, wherein forming two layers, one layer as aconductive layer and the other layer as a plane of high permeabilitymaterial, includes forming the conductive layer as a metal conductiveplane closer to the transmission line than the plane of highpermeability material.
 36. A method for forming transmission lines in anintegrated circuit, comprising: forming a layer of insulating materialdisposed above a substrate; forming a transmission line in the layer ofinsulating material, the transmission line having at least one surfacelayer formed of a magnetic material containing a ferrite encasing thetransmission line on at least three sides; forming a pair of conductivemetal lines in the layer of insulating material, the pair of conductivemetal lines formed such that the transmission line is interposed betweenand parallel with the pair of conductive metal lines; and forming aconductive plane on the layer of insulating material, wherein formingthe conductive plane includes forming two layers, one layer as aconductive layer and the other layer as a plane of magnetic material.37. The method of claim 36, wherein the method further includes forminga composite hexaferrite as the ferrite of the magnetic material formedas at least one surface layer of the transmission line.
 38. The methodof claim 36, wherein the method further includes forming a Co₂Z ferriteas the ferrite of the magnetic material formed as at least one surfacelayer of the transmission line.
 39. The method of claim 36, wherein themethod further includes forming a composite hexaferrite containing(1−x)Ba₃Co₂Fe₂₄O₄₁+x(Ni_(0.60)Zn_(0.20)Cu_(0.20))Fe₂O₄+0.5 wt % Bi₂O₃with x substantially equal to 0.1 as the ferrite of the magneticmaterial formed as at least one surface layer of the transmission line.40. The method of claim 36, wherein the method further includes forminga composite hexaferrite containing(1−x)Ba₃Co₂Fe₂₄O₄₁+x(Ni_(0.60)Zn_(0.20)Cu_(0.20))Fe₂O₄+0.5 wt % Bi₂O₃with x substantially equal to 0.2 as the ferrite of the magneticmaterial formed as at least one surface layer of the transmission line.41. The method of claim 36, wherein the method further includes forminga number of transmission lines interposed among and parallel with anumber of conductive metal lines, each transmission line having at leastone surface layer formed of a magnetic material encasing the conductivemetal line on at least three sides.
 42. The method of claim 36, whereinthe method further includes forming the pair of conductive metal linescoupled to ground.
 43. The method of claim 36, wherein the methodfurther includes encasing the transmission line on at least three sideswith two sides of the three encasing sides parallel to the pair ofconductive metal lines and the third side adjacent the substrate. 44.The method of claim 36, wherein the method further includes forming afirst conductive plane on the substrate and the layer of insulatingmaterial on the first conductive plane.
 45. The method of claim 44,wherein the method further includes forming the first conductive planehaving a metal ground plane.
 46. A method for forming transmission linesin an integrated circuit, comprising: forming a first layer ofinsulating material disposed above a substrate; forming a transmissionline on the first layer of insulating material, the transmission linehaving at least one surface layer formed of a film of high permeabilitymaterial containing a ferrite encasing the transmission line on at leastthree sides; forming a pair of conductive metal lines on the first layerof insulating material, each conductive metal line having at least onesurface layer formed of a film of the high permeability materialcontaining a ferrite encasing the conductive metal line on at leastthree sides, wherein the pair of conductive metal lines are formed suchthat the transmission line is interposed between and parallel with thepair of conductive metal lines; forming a second layer of insulatingmaterial on the transmission line and the pair of conductive metallines; and forming a conductive plane on the second layer of insulatingmaterial, wherein forming the conductive plane includes forming twolayers, one layer as a conductive layer and the other layer as a planeof high permeability material.
 47. The method of claim 46, wherein themethod further includes forming a composite hexaferrite as the ferriteof the transmission line and each conductive metal line.
 48. The methodof claim 46, wherein the method further includes forming a Co₂Z ferriteas the ferrite of the transmission line and each conductive metal line.49. The method of claim 46, wherein the method further includes forminga composite hexaferrite containing(1−x)Ba₃Co₂Fe₂₄O₄₁+x(Ni_(0.60)Zn_(0.20)Cu_(0.20))Fe₂O₄+0.5 wt % Bi₂O₃with x substantially equal to 0.1 as the fenite of the transmission lineand each conductive metal line.
 50. The method of claim 46, wherein themethod further includes forming a composite hexaferrite containing(1−x)Ba₃Co₂Fe₂₄O₄₁+x(Ni_(0.60)Zn_(0.20)Cu_(0.20))Fe₂O₄+0.5 wt % Bi₂O₃with x substantially equal to 0.2 as the ferrite of the transmissionline and each conductive metal line.
 51. The method of claim 46, whereinthe method further includes forming a number of transmission linesinterposed among and parallel with a number of conductive metal lines,each conductive metal line having at least one surface layer formed of ahigh permeability material encasing the conductive metal line on atleast three sides, each transmission line having at least one surfacelayer formed of a high permeability material encasing the conductivemetal line on at least three sides.
 52. The method of claim 46, whereinthe method further includes forming the pair of conductive metal linescoupled to ground.
 53. The method of claim 46, wherein the methodfurther includes forming the transmission line such that the three sidesencasing the transmission line are configured with two sides parallel tothe pair of conductive metal lines and the third side adjacent thesubstrate and forming the pair of conductive metal lines such that thethree sides encasing each conductive metal line are configured with twosides parallel to the transmission line and the third side adjacent thesubstrate.
 54. The method of claim 46, wherein the method furtherincludes forming a first conductive plane on the substrate and the firstlayer of insulating material on the first conductive plane.
 55. Themethod of claim 46, wherein the method further includes forming thefirst conductive plane having a metal ground plane.
 56. A method forforming transmission lines in an integrated circuit, comprising: forminga layer of insulating material disposed above a substrate; forming atransmission line in the layer of insulating material, the transmissionline having at least one surface layer formed of a magnetic materialcontaining a ferrite encasing the transmission line on two sides;forming a pair of high permeability metal lines in the layer ofinsulating material, the pair of magnetic metal lines formed such thatthe transmission line is interposed between and parallel with the pairof magnetic metal lines; and forming a second layer of insulatingmaterial on the transmission line and the pair of conductive metallines.
 57. The method of claim 56, wherein the method further includesforming the two sides encasing the transmission line with magneticmaterial as opposing sides with one of the two sides adjacent thesubstrate.
 58. The method of claim 56, wherein the method furtherincludes forming a first conductive plane on the substrate, wherein thelayer of insulating material is formed on the first conductive plane.59. The method of claim 58, wherein the method further includes forminga second conductive plane on the second layer of insulating material.60. The method of claim 59, wherein the method further includes formingthe two sides encasing the transmission line adjacent to the first andsecond conductive planes.
 61. The method of claim 60, wherein the methodfurther includes coupling the second conductive plane to a power supply.62. The method of claim 56, wherein forming a pair of magnetic metallines includes forming metal lines containing a composite hexaferrite.63. The method of claim 56, wherein the method further includes forminga composite hexaferrite as the ferrite of the magnetic material formedas at least one surface layer of the transmission line.
 64. The methodof claim 56, wherein the method further includes forming a Co₂Z ferriteas the ferrite of the magnetic material formed as at least one surfacelayer of the transmission line.
 65. The method of claim 56, wherein themethod further includes forming a composite hexaferrite containing(1−x)Ba₃Co₂Fe₂₄O₄₁+x(Ni_(0.60)Zn_(0.20)Cu_(0.20))Fe₂O₄+0.5 wt % Bi₂O₃with x substantially equal to 0.1 as the ferrite of the magneticmaterial formed as at least one surface layer of the transmission line.66. The method of claim 56, wherein the method further includes forminga composite hexaferrite containing(1−x)Ba₃Co₂Fe₂₄O₄₁+x(Ni_(0.60)Zn_(0.20)Cu_(0.20))Fe₂O₄+0.5 wt % Bi₂O₃with x substantially equal to 0.2 as the ferrite of the magneticmaterial formed as at least one surface layer of the transmission line.67. The method of claim 56, wherein the method further includes forminga number of transmission lines interposed among and parallel with anumber of magnetic metal lines, each transmission line having at leastone surface layer formed of a magnetic material containing a ferriteencasing the transmission line on two sides.
 68. The method of claim 56,wherein the method further includes coupling the pair of magnetic metallines to ground.
 69. The method of claim 56, wherein the method furtherincludes forming a pair of magnetic metal lines and forming the magneticmaterial of the surface layer encasing the transmission line on twosides from the same high permeability material.
 70. A method for formingtransmission lines in an integrated circuit, comprising: forming a firstconductive plane on a substrate; forming a first layer of insulatingmaterial on the first conductive plane; forming a transmission line onthe first layer of insulating material; forming a pair of conductivemetal lines on the first layer of insulating material, the pair ofconductive metal lines formed such that the transmission line isinterposed between and parallel with the pair of conductive metal lines,wherein each conductive metal line has at least one surface layer formedof a high permeability material containing a ferrite encasing theconductive metal line on at least three sides; forming a second layer ofinsulating material on the transmission line and the pair of conductivemetal lines; and forming a second conductive plane on the second layerof insulating material, wherein forming at least one of the first andsecond conductive planes includes forming two layers, one layer as aconductive layer and the other layer as a plane of high permeabilitymaterial.
 71. The method of claim 70, wherein the method furtherincludes forming a composite hexaferrite as the ferrite of the highpermeability material formed as at least one surface layer of eachconductive metal line.
 72. The method of claim 70, wherein the methodfurther includes forming a Co₂Z ferrite as the ferrite of the highpermeability material formed as at least one surface layer of eachconductive metal line.
 73. The method of claim 70, wherein the methodfurther includes forming a composite hexaferrite containing(1−x)Ba₃Co₂Fe₂₄O₄₁+x(Ni_(0.60)Zn_(0.20)Cu_(0.20))Fe₂O₄+0.5 wt % Bi₂O₃with x substantially equal to 0.1 as the ferrite of the highpermeability material formed as at least one surface layer of eachconductive metal line.
 74. The method of claim 70, wherein the methodfurther includes forming a composite hexaferrite containing(1−x)Ba₃Co₂Fe₂₄O₄₁+x(Ni_(0.60)Zn_(0.20)Cu_(0.20))Fe₂O₄+0.5 wt % Bi₂O₃with x substantially equal to 0.2 as the ferrite of the highpermeability material formed as at least one surface layer of eachconductive metal line.
 75. The method of claim 70, wherein the methodfurther includes forming a number of transmission lines interposed amongand parallel with a number of high permeability metal lines, eachconductive metal line having at least one surface layer formed of a highpermeability material containing a ferrite encasing the conductive metalline on at least three sides.
 76. The method of claim 70, whereinforming two layers, one layer as a conductive layer and the other layeras a plane of high permeability material includes forming the conductivelayer as a metal ground plane and the plane of high permeabilitymaterial as a film containing a composite hexaferrite.
 77. The method ofclaim 70, wherein forming the first and second conductive planesincludes forming both the first and the second conductive plane as twolayers, one layer as a conductive layer and the other layer as a planeof high permeability material, the high permeability material being thesame as for the high permeability material encasing each conductivemetal line on at least three sides.
 78. The method of claim 70, whereinforming two layers, one layer as a conductive layer and the other layeras a plane of high permeability material, includes forming theconductive layer with a resistance lower than the plane of highpermeability material.
 79. The method of claim 70, wherein forming twolayers, one layer as a conductive layer and the other layer as a planeof high permeability material, includes forming the conductive layer asa metal conductive plane with the plane of high permeability materialcloser to the transmission line than the metal conductive plane.
 80. Themethod of claim 70, wherein forming two layers, one layer as aconductive layer and the other layer as a plane of high permeabilitymaterial, includes forming the conductive layer as a metal conductiveplane closer to the transmission line than the plane of highpermeability material.
 81. The method of claim 70, wherein the methodfurther includes encasing each conductive metal line on at least threesides such that two sides of the three sides are parallel to thetransmission line.
 82. A method for forming transmission lines in anintegrated circuit, comprising: forming an insulating layer disposedabove a substrate; forming a pair of conductive metal lines in theinsulating layer; forming a transmission line in the insulating layer,the transmission line interposed between and parallel with the pair ofconductive metal lines, wherein at least one of the transmission lineand the conductive lines has a magnetic material containing a ferrite.83. The method of claim 82, wherein the method further includes forminga Co₂Z ferrite as the ferrite.
 84. The method of claim 82, wherein themethod further includes forming a composite hexaferrite as the ferrite.85. The method of claim 82, wherein the method further includes forminga composite hexaferrite containing(1−x)Ba₃Co₂Fe₂₄O₄₁+x(Ni_(0.60)Zn_(0.20)Cu_(0.20))Fe₂O₄+0.5 wt % Bi₂O₃with x substantially equal to 0.1 as the ferrite.
 86. The method ofclaim 82, wherein the method further includes forming a compositehexaferrite containing(1−x)Ba₃Co₂Fe₂₄O₄₁+x(Ni_(0.60)Zn_(0.20)Cu_(0.20))Fe₂O₄+0.5 wt % Bi₂O₃with x substantially equal to 0.2 as the ferrite.